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Vulnerability record · CVE-2021-41611 · published 18 October 2021

CVE-2021-41611: Squid-cache squid improper certificate validation vulnerability

Squid Cache · Squid

An issue was discovered in Squid 5.0.6 through 5.1.x before 5.2. When validating an origin server or peer certificate, Squid may incorrectly classify certain certificates as trusted. This problem allows a remote server to obtain security trust well improperly. This indication of trust may be passed along to clients, allowing access to unsafe or hijacked services.

7.5 CVSS 3.1 High EPSS 2.9% · top 13.3% CWE-295 · Improper certificate validation
7.5CVSS 3.1 base score, v2 5.0
2.9%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
8References
17 Jun 2026Last modified by NVD

Description

An issue was discovered in Squid 5.0.6 through 5.1.x before 5.2. When validating an origin server or peer certificate, Squid may incorrectly classify certain certificates as trusted. This problem allows a remote server to obtain security trust well improperly. This indication of trust may be passed along to clients, allowing access to unsafe or hijacked services.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://www.openwall.com/lists/oss-security/2021/12/23/2 Mailing ListThird Party Advisory
http://www.squid-cache.org/Versions/v6/changesets/squid-6-43d6b5c81b88ec2256b430c69a872a1e4f324e4a.patch Vendor Advisory
https://github.com/squid-cache/squid/security/advisories/GHSA-47m4-g3mv-9q5r PatchThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CWQ2WKDWTSO47S3F6XJJ6HG
http://www.openwall.com/lists/oss-security/2021/12/23/2 Mailing ListThird Party Advisory
http://www.squid-cache.org/Versions/v6/changesets/squid-6-43d6b5c81b88ec2256b430c69a872a1e4f324e4a.patch Vendor Advisory
https://github.com/squid-cache/squid/security/advisories/GHSA-47m4-g3mv-9q5r PatchThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CWQ2WKDWTSO47S3F6XJJ6HG

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-41611), CISA KEV, FIRST EPSS (scores of 2026-10-03). This page is refreshed as NVD updates the record.